Field of the Invention
The invention relates to new electron transporting compounds and electrophotographic compositions and elements comprising electron transporting compounds.
Electrophotographic layers and elements have been extensively described in both the patent and other literature. Generally, imaging processes involving these elements have in common the steps of electrostatically charging an electrophotographic element and exposing the element imagewise to electromagnetic radiation, thereby forming an electrostatic charge image. A variety of subsequent operations, well known in the art, can then be employed to produce a permanent record of the image.
Upon exposure of an electrostatically charged electrophotographic element, electron-hole pairs are formed in the electrophotographic layer of the element. When the element is electrostatically charged with a negative potential, the hole migrates to the surface of the electrophotographic layer thereby discharging the layer in the exposed areas. When the electrophotographic element is charged with a positive potential the electron migrates toward the surface of the electrophotographic layer thereby discharging the layer imagewise in the exposed areas.
Numerous electron donating organic photoconductive compounds are known which are effective in transporting holes to the surface of an electrophotographic layer. However, only a few electron accepting materials are effective in electron transport. An example is 2,4,7-trinitro-9-fluorenone (TNF). Thus, in most electrophotographic processes the electrophotographic element is initially charged to a negative potential.
There are applications in which it is more desirable to charge the electrophotographic element with a positive potential because of the lack of high quality negatively charged toners, such as in laser printing.
However, TNF is not equally effective as an electron transporting agent in all electrophotographic layers and elements designed for these uses. In addition, TNF is a known carcinogenic material.